There are a number of known processes for ammoxidation reactions of organic compounds. The present invention relates to reactions using a metal oxide catalyst at a temperature of from 300.degree. C. to 600.degree. C. Examples of organic compounds include olefinic hydrocarbons, alcohols, aldehydes, alkyl substituted aromatic hydrocarbons, and alkyl substituted heterocyclic compounds having nitrogen, oxygen and sulfur, etc., as hetero atoms.
It has been described in U.S. Pat. Nos. 2,904,580, 3,152,170, 3,094,565, 3,094,552, 3,197,419, 3,308,151, 3,911,089, 4,139,552, 3,542,843, 3,591,620, etc., that metal oxide catalysts containing molybdenum and bismuth, etc., and metal oxide catalysts containing antimony and tin, iron or uranium are useful for ammoxidation of propylene, isobutene and methanol, etc. It has been described in U.S. Pat. Nos. 2,499,055, 2,838,558, 2,510,605, 3,959,297, etc., that metal oxide catalysts containing vanadium are useful for ammoxidation of alkyl substituted aromatic hydrocarbons or alkyl substituted heterocyclic compounds.
During the ammoxidation of these organic compounds, the activity of the catalyst often deteriorates after being used for a long period of time. The degree of deterioration varies with the kind of catalyst and the conditions under which the catalyst is used.
The activity deterioration has various causes. Accordingly, a number of different approaches have been investigated with respect to eliminating the deterioration.
However, the specific reason for the deterioration is not always obvious which makes it difficult to determine a method of eliminating the deterioration. Some examples of proposed methods require change of the reaction condition, partial replacement of the catalyst, exchange of all the catalysts, or regeneration of the deteriorated catalyst taken out of the reactor. Such methods have not been found to be economical.
It is very advantageous if activity of the catalyst is maintained or recovered without adding a fresh catalyst or interrupting the reaction.
As to this, U.S. Pat. No. 3,882,159 discloses a process for regenerating catalysts which comprises contacting in situ a molybdenum containing fluidized-bed catalyst which has become deteriorated by loss of molybdenum during an ammoxidation reaction of propylene with fluidized-bed particles composed of an essentially inert carrier and molybdenum oxide at the reaction temperature. This U.S. Patent is concerned with only regeneration of a molybdenum containing fluidized-bed catalyst, wherein molybdenum oxide supported on an inert carrier is simply used as the regenerating agent.
U.S. Pat. No. 3,236,782 discloses a process for regenerating metal oxide catalysts containing at least Cr, V, Mo or W which comprises contacting the catalyst with a vapor of a compound of the same metal as that present in the catalyst. The process disclosed in this U.S. Patent requires a complicated operation in that the catalyst component is introduced as a vapor into the reaction zone.